/* packet-mongo.c
 * Routines for Mongo Wire Protocol dissection
 * Copyright 2010, Alexis La Goutte <alexis.lagoutte at gmail dot com>
 * BSON dissection added 2011, Thomas Buchanan <tom at thomasbuchanan dot com>
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

/*
 * See Mongo Wire Protocol Specification
 * https://www.mongodb.com/docs/manual/reference/mongodb-wire-protocol/
 * See also BSON Specification
 * http://bsonspec.org/spec.html
 */

#include "config.h"

#include <epan/packet.h>
#include <epan/tfs.h>
#include <wsutil/array.h>
#include <epan/expert.h>
#include <epan/proto_data.h>
#include <epan/exceptions.h>
#include <wsutil/crc32.h> // CRC32C_PRELOAD
#include <epan/crc32-tvb.h> // crc32c_tvb_offset_calculate
#include "packet-tcp.h"
#ifdef HAVE_SNAPPY
#include <snappy-c.h>
#endif

void proto_register_mongo(void);
void proto_reg_handoff_mongo(void);

static dissector_handle_t mongo_handle;
static dissector_handle_t mongo_heur_handle;

/* Forward declaration */
static int
dissect_opcode_types(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *mongo_tree, unsigned opcode, unsigned *effective_opcode, uint8_t **command_name);

/* This is not IANA assigned nor registered */
#define TCP_PORT_MONGO 27017

/* All opcodes other than OP_COMPRESSED and OP_MSG were removed
 * in MongoDB 5.1 (December 2021)
 */
#define OP_REPLY           1
#define OP_MESSAGE      1000
#define OP_UPDATE       2001
#define OP_INSERT       2002
#define OP_RESERVED     2003
#define OP_QUERY        2004
#define OP_GET_MORE     2005
#define OP_DELETE       2006
#define OP_KILL_CURSORS 2007
#define OP_COMMAND      2010
#define OP_COMMANDREPLY 2011
#define OP_COMPRESSED   2012
#define OP_MSG          2013

/**************************************************************************/
/*                      OpCode                                            */
/**************************************************************************/
static const value_string opcode_vals[] = {
  { OP_REPLY,  "Reply" },
  { OP_MESSAGE, "Message" },
  { OP_UPDATE,  "Update document" },
  { OP_INSERT,  "Insert document" },
  { OP_RESERVED,"Reserved" },
  { OP_QUERY,  "Query" },
  { OP_GET_MORE,  "Get More" },
  { OP_DELETE,  "Delete document" },
  { OP_KILL_CURSORS,  "Kill Cursors" },
  { OP_COMMAND,  "Command Request" },
  { OP_COMMANDREPLY,  "Command Reply" },
  { OP_COMPRESSED,  "Compressed Data" },
  { OP_MSG,  "Extensible Message Format" },
  { 0,  NULL }
};

#define KIND_BODY               0
#define KIND_DOCUMENT_SEQUENCE  1

/**************************************************************************/
/*                      Section Kind                                      */
/**************************************************************************/
static const value_string section_kind_vals[] = {
  { KIND_BODY, "Body" },
  { KIND_DOCUMENT_SEQUENCE, "Document Sequence" },
  { 0,  NULL }
};

/**************************************************************************/
/*                      Compression Engines                               */
/**************************************************************************/
#define MONGO_COMPRESSOR_NOOP    0
#define MONGO_COMPRESSOR_SNAPPY  1
#define MONGO_COMPRESSOR_ZLIB    2
#define MONGO_COMPRESSOR_ZSTD    3

static const value_string compressor_vals[] = {
  { MONGO_COMPRESSOR_NOOP,   "Noop (Uncompressed)" },
  { MONGO_COMPRESSOR_SNAPPY, "Snappy" },
  { MONGO_COMPRESSOR_ZLIB,   "Zlib" },
  { MONGO_COMPRESSOR_ZSTD,   "Zstd" },
  { 0,  NULL }
};

/* BSON Element types */
/* See http://bsonspec.org/#/specification for detail */
#define BSON_ELEMENT_TYPE_DOUBLE         1
#define BSON_ELEMENT_TYPE_STRING         2
#define BSON_ELEMENT_TYPE_DOC            3
#define BSON_ELEMENT_TYPE_ARRAY          4
#define BSON_ELEMENT_TYPE_BINARY         5
#define BSON_ELEMENT_TYPE_UNDEF          6  /* Deprecated */
#define BSON_ELEMENT_TYPE_OBJ_ID         7
#define BSON_ELEMENT_TYPE_BOOL           8
#define BSON_ELEMENT_TYPE_DATETIME       9
#define BSON_ELEMENT_TYPE_NULL          10
#define BSON_ELEMENT_TYPE_REGEX         11
#define BSON_ELEMENT_TYPE_DB_PTR        12  /* Deprecated */
#define BSON_ELEMENT_TYPE_JS_CODE       13
#define BSON_ELEMENT_TYPE_SYMBOL        14
#define BSON_ELEMENT_TYPE_JS_CODE_SCOPE 15
#define BSON_ELEMENT_TYPE_INT32         16  /* 0x10 */
#define BSON_ELEMENT_TYPE_TIMESTAMP     17  /* 0x11 */
#define BSON_ELEMENT_TYPE_INT64         18  /* 0x12 */
#define BSON_ELEMENT_TYPE_DECIMAL128    19  /* 0x13 */
#define BSON_ELEMENT_TYPE_MIN_KEY      255  /* 0xFF */
#define BSON_ELEMENT_TYPE_MAX_KEY      127  /* 0x7F */

static const value_string element_type_vals[] = {
  { BSON_ELEMENT_TYPE_DOUBLE,         "Double" },
  { BSON_ELEMENT_TYPE_STRING,         "String" },
  { BSON_ELEMENT_TYPE_DOC,            "Document" },
  { BSON_ELEMENT_TYPE_ARRAY,          "Array" },
  { BSON_ELEMENT_TYPE_BINARY,         "Binary" },
  { BSON_ELEMENT_TYPE_UNDEF,          "Undefined" },
  { BSON_ELEMENT_TYPE_OBJ_ID,         "Object ID" },
  { BSON_ELEMENT_TYPE_BOOL,           "Boolean" },
  { BSON_ELEMENT_TYPE_DATETIME,       "Datetime" },
  { BSON_ELEMENT_TYPE_NULL,           "NULL" },
  { BSON_ELEMENT_TYPE_REGEX,          "Regular Expression" },
  { BSON_ELEMENT_TYPE_DB_PTR,         "DBPointer" },
  { BSON_ELEMENT_TYPE_JS_CODE,        "JavaScript Code" },
  { BSON_ELEMENT_TYPE_SYMBOL,         "Symbol" },
  { BSON_ELEMENT_TYPE_JS_CODE_SCOPE,  "JavaScript Code w/Scope" },
  { BSON_ELEMENT_TYPE_INT32,          "Int32" },
  { BSON_ELEMENT_TYPE_TIMESTAMP,      "Timestamp" },
  { BSON_ELEMENT_TYPE_INT64,          "Int64" },
  { BSON_ELEMENT_TYPE_DECIMAL128,     "128-bit decimal floating point" },
  { BSON_ELEMENT_TYPE_MIN_KEY,        "Min Key" },
  { BSON_ELEMENT_TYPE_MAX_KEY,        "Max Key" },
  { 0, NULL }
};

/* BSON Element Binary subtypes */
#define BSON_ELEMENT_BINARY_TYPE_GENERIC  0
#define BSON_ELEMENT_BINARY_TYPE_FUNCTION 1
#define BSON_ELEMENT_BINARY_TYPE_BINARY   2 /* OLD */
#define BSON_ELEMENT_BINARY_TYPE_UUID     3
#define BSON_ELEMENT_BINARY_TYPE_MD5      4
#define BSON_ELEMENT_BINARY_TYPE_USER   128 /* 0x80 */

#if 0
static const value_string binary_type_vals[] = {
  { BSON_ELEMENT_BINARY_TYPE_GENERIC,  "Generic" },
  { BSON_ELEMENT_BINARY_TYPE_FUNCTION, "Function" },
  { BSON_ELEMENT_BINARY_TYPE_BINARY,   "Binary" },
  { BSON_ELEMENT_BINARY_TYPE_UUID,     "UUID" },
  { BSON_ELEMENT_BINARY_TYPE_MD5,      "MD5" },
  { BSON_ELEMENT_BINARY_TYPE_USER,     "User" },
  { 0, NULL }
};
#endif

static int proto_mongo;
static int hf_mongo_message_length;
static int hf_mongo_request_id;
static int hf_mongo_response_to;
static int hf_mongo_op_code;
static int hf_mongo_fullcollectionname;
static int hf_mongo_database_name;
static int hf_mongo_collection_name;
static int hf_mongo_reply_flags;
static int hf_mongo_reply_flags_cursornotfound;
static int hf_mongo_reply_flags_queryfailure;
static int hf_mongo_reply_flags_sharedconfigstale;
static int hf_mongo_reply_flags_awaitcapable;
static int hf_mongo_cursor_id;
static int hf_mongo_starting_from;
static int hf_mongo_number_returned;
static int hf_mongo_message;
static int hf_mongo_zero;
static int hf_mongo_update_flags;
static int hf_mongo_update_flags_upsert;
static int hf_mongo_update_flags_multiupdate;
static int hf_mongo_selector;
static int hf_mongo_update;
static int hf_mongo_insert_flags;
static int hf_mongo_insert_flags_continueonerror;
static int hf_mongo_query_flags;
static int hf_mongo_query_flags_tailablecursor;
static int hf_mongo_query_flags_slaveok;
static int hf_mongo_query_flags_oplogreplay;
static int hf_mongo_query_flags_nocursortimeout;
static int hf_mongo_query_flags_awaitdata;
static int hf_mongo_query_flags_exhaust;
static int hf_mongo_query_flags_partial;
static int hf_mongo_number_to_skip;
static int hf_mongo_number_to_return;
static int hf_mongo_query;
static int hf_mongo_return_field_selector;
static int hf_mongo_document;
static int hf_mongo_document_length;
static int hf_mongo_document_empty;
static int hf_mongo_delete_flags;
static int hf_mongo_delete_flags_singleremove;
static int hf_mongo_number_of_cursor_ids;
static int hf_mongo_elements;
static int hf_mongo_element_name;
static int hf_mongo_element_type;
static int hf_mongo_element_length;
static int hf_mongo_element_value_boolean;
static int hf_mongo_element_value_int32;
static int hf_mongo_element_value_int64;
static int hf_mongo_element_value_decimal128;
static int hf_mongo_element_value_double;
static int hf_mongo_element_value_string;
static int hf_mongo_element_value_string_length;
static int hf_mongo_element_value_binary;
static int hf_mongo_element_value_binary_length;
static int hf_mongo_element_value_regex_pattern;
static int hf_mongo_element_value_regex_options;
static int hf_mongo_element_value_objectid;
static int hf_mongo_element_value_objectid_time;
static int hf_mongo_element_value_objectid_host;
static int hf_mongo_element_value_objectid_pid;
static int hf_mongo_element_value_objectid_machine_id;
static int hf_mongo_element_value_objectid_inc;
static int hf_mongo_element_value_db_ptr;
static int hf_mongo_element_value_js_code;
static int hf_mongo_element_value_js_scope;
static int hf_mongo_database;
static int hf_mongo_commandname;
static int hf_mongo_metadata;
static int hf_mongo_commandargs;
static int hf_mongo_commandreply;
static int hf_mongo_outputdocs;
static int hf_mongo_unknown;
static int hf_mongo_compression_info;
static int hf_mongo_original_op_code;
static int hf_mongo_uncompressed_size;
static int hf_mongo_compressor;
static int hf_mongo_compressed_data;
static int hf_mongo_unsupported_compressed;
static int hf_mongo_msg_flags;
static int hf_mongo_msg_flags_checksumpresent;
static int hf_mongo_msg_flags_moretocome;
static int hf_mongo_msg_flags_exhaustallowed;
static int hf_mongo_msg_sections_section;
static int hf_mongo_msg_sections_section_kind;
static int hf_mongo_msg_sections_section_body;
static int hf_mongo_msg_sections_section_doc_sequence;
static int hf_mongo_msg_sections_section_size;
static int hf_mongo_msg_sections_section_doc_sequence_id;
static int hf_mongo_msg_checksum;
static int hf_mongo_msg_checksum_status;

static int ett_mongo;
static int ett_mongo_doc;
static int ett_mongo_elements;
static int ett_mongo_element;
static int ett_mongo_objectid;
static int ett_mongo_machine_id;
static int ett_mongo_code;
static int ett_mongo_fcn;
static int ett_mongo_flags;
static int ett_mongo_compression_info;
static int ett_mongo_sections;
static int ett_mongo_section;
static int ett_mongo_msg_flags;
static int ett_mongo_doc_sequence;

static expert_field ei_mongo_document_recursion_exceeded;
static expert_field ei_mongo_document_length_bad;
static expert_field ei_mongo_section_size_bad;
static expert_field ei_mongo_unknown;
static expert_field ei_mongo_unsupported_compression;
static expert_field ei_mongo_msg_checksum;

static int
dissect_fullcollectionname(tvbuff_t *tvb, unsigned offset, proto_tree *tree)
{
  int32_t fcn_length, dbn_length;
  proto_item *ti;
  proto_tree *fcn_tree;

  fcn_length = tvb_strsize(tvb, offset);
  ti = proto_tree_add_item(tree, hf_mongo_fullcollectionname, tvb, offset, fcn_length, ENC_ASCII);

  /* If this doesn't find anything, we'll just throw an exception below */
  dbn_length = tvb_find_uint8(tvb, offset, fcn_length, '.') - offset;

  fcn_tree = proto_item_add_subtree(ti, ett_mongo_fcn);

  proto_tree_add_item(fcn_tree, hf_mongo_database_name, tvb, offset, dbn_length, ENC_ASCII);

  proto_tree_add_item(fcn_tree, hf_mongo_collection_name, tvb, offset + 1 + dbn_length, fcn_length - dbn_length - 2, ENC_ASCII);

  return fcn_length;
}

/* http://docs.mongodb.org/manual/reference/limits/ */
/* http://www.mongodb.org/display/DOCS/Documents */
#define BSON_MAX_NESTING 100
#define BSON_MAX_DOC_SIZE (16 * 1000 * 1000)
static int
// NOLINTNEXTLINE(misc-no-recursion)
dissect_bson_document(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree, int hf_mongo_doc)
{
  int32_t document_length;
  unsigned final_offset;
  proto_item *ti, *elements, *element, *objectid, *js_code, *js_scope, *machine_id;
  proto_tree *doc_tree, *elements_tree, *element_sub_tree, *objectid_sub_tree, *js_code_sub_tree, *js_scope_sub_tree, *machine_id_sub_tree;

  document_length = tvb_get_letohl(tvb, offset);

  ti = proto_tree_add_item(tree, hf_mongo_doc, tvb, offset, document_length, ENC_NA);
  doc_tree = proto_item_add_subtree(ti, ett_mongo_doc);

  proto_tree_add_item(doc_tree, hf_mongo_document_length, tvb, offset, 4, ENC_LITTLE_ENDIAN);

  if (document_length < 5) {
      expert_add_info_format(pinfo, ti, &ei_mongo_document_length_bad, "BSON document length too short: %u", document_length);
      return MAX(4, document_length); /* see the comment above */
  }

  if (document_length > BSON_MAX_DOC_SIZE) {
      expert_add_info_format(pinfo, ti, &ei_mongo_document_length_bad, "BSON document length too long: %u", document_length);
      return document_length;
  }

  if (document_length == 5) {
    /* document with length 5 is an empty document */
    /* don't display the element subtree */
    proto_tree_add_item(doc_tree, hf_mongo_document_empty, tvb, offset, document_length, ENC_NA);
    return document_length;
  }

  unsigned nest_level = p_get_proto_depth(pinfo, proto_mongo);
  if (++nest_level > BSON_MAX_NESTING) {
      expert_add_info_format(pinfo, ti, &ei_mongo_document_recursion_exceeded, "BSON document recursion exceeds %u", BSON_MAX_NESTING);
      /* return the number of bytes we consumed, these are at least the 4 bytes for the length field */
      return MAX(4, document_length);
  }
  p_set_proto_depth(pinfo, proto_mongo, nest_level);

  final_offset = offset + document_length;
  offset += 4;

  elements = proto_tree_add_item(doc_tree, hf_mongo_elements, tvb, offset, document_length-5, ENC_NA);
  elements_tree = proto_item_add_subtree(elements, ett_mongo_elements);

  do {
    /* Read document elements */
    uint8_t e_type;  /* Element type */
    int str_len = -1;   /* String length */
    int e_len = -1;     /* Element length */
    int doc_len = -1;   /* Document length */

    e_type = tvb_get_uint8(tvb, offset);
    tvb_get_stringz_enc(pinfo->pool, tvb, offset+1, &str_len, ENC_ASCII);

    element = proto_tree_add_item(elements_tree, hf_mongo_element_name, tvb, offset+1, str_len-1, ENC_UTF_8);
    element_sub_tree = proto_item_add_subtree(element, ett_mongo_element);
    proto_tree_add_item(element_sub_tree, hf_mongo_element_type, tvb, offset, 1, ENC_LITTLE_ENDIAN);

    offset += str_len+1;

    switch(e_type) {
      case BSON_ELEMENT_TYPE_DOUBLE:
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_double, tvb, offset, 8, ENC_LITTLE_ENDIAN);
        offset += 8;
        break;
      case BSON_ELEMENT_TYPE_STRING:
      case BSON_ELEMENT_TYPE_JS_CODE:
      case BSON_ELEMENT_TYPE_SYMBOL:
        str_len = tvb_get_letohl(tvb, offset);
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_string_length, tvb, offset, 4, ENC_LITTLE_ENDIAN);
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_string, tvb, offset+4, str_len, ENC_UTF_8);
        offset += str_len+4;
        break;
      case BSON_ELEMENT_TYPE_DOC:
      case BSON_ELEMENT_TYPE_ARRAY:
        offset += dissect_bson_document(tvb, pinfo, offset, element_sub_tree, hf_mongo_document);
        break;
      case BSON_ELEMENT_TYPE_BINARY:
        e_len = tvb_get_letohl(tvb, offset);
        /* TODO - Add functions to decode various binary subtypes */
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_binary_length, tvb, offset, 4, ENC_LITTLE_ENDIAN);
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_binary, tvb, offset+5, e_len, ENC_NA);
        offset += e_len+5;
        break;
      case BSON_ELEMENT_TYPE_UNDEF:
      case BSON_ELEMENT_TYPE_NULL:
      case BSON_ELEMENT_TYPE_MIN_KEY:
      case BSON_ELEMENT_TYPE_MAX_KEY:
        /* Nothing to do, as there is no element content */
        break;
      case BSON_ELEMENT_TYPE_OBJ_ID:
        objectid = proto_tree_add_item(element_sub_tree, hf_mongo_element_value_objectid, tvb, offset, 12, ENC_NA);
        objectid_sub_tree = proto_item_add_subtree(objectid, ett_mongo_objectid);
        /* Unlike most BSON elements, parts of ObjectID are stored Big Endian, so they can be compared bit by bit */
        proto_tree_add_item(objectid_sub_tree, hf_mongo_element_value_objectid_time, tvb, offset, 4, ENC_BIG_ENDIAN);
        /* The machine ID was traditionally split up in Host Hash/PID */
        machine_id = proto_tree_add_item(objectid_sub_tree, hf_mongo_element_value_objectid_machine_id, tvb, offset+4, 5, ENC_NA);
        machine_id_sub_tree = proto_item_add_subtree(machine_id, ett_mongo_machine_id);
        proto_tree_add_item(machine_id_sub_tree, hf_mongo_element_value_objectid_host, tvb, offset+4, 3, ENC_LITTLE_ENDIAN);
        proto_tree_add_item(machine_id_sub_tree, hf_mongo_element_value_objectid_pid, tvb, offset+7, 2, ENC_LITTLE_ENDIAN);

        proto_tree_add_item(objectid_sub_tree, hf_mongo_element_value_objectid_inc, tvb, offset+9, 3, ENC_BIG_ENDIAN);
        offset += 12;
        break;
      case BSON_ELEMENT_TYPE_BOOL:
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_boolean, tvb, offset, 1, ENC_NA);
        offset += 1;
        break;
      case BSON_ELEMENT_TYPE_REGEX:
        /* regex pattern */
        tvb_get_stringz_enc(pinfo->pool, tvb, offset, &str_len, ENC_ASCII);
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_regex_pattern, tvb, offset, str_len, ENC_UTF_8);
        offset += str_len;
        /* regex options */
        tvb_get_stringz_enc(pinfo->pool, tvb, offset, &str_len, ENC_ASCII);
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_regex_options, tvb, offset, str_len, ENC_UTF_8);
        offset += str_len;
        break;
      case BSON_ELEMENT_TYPE_DB_PTR:
        str_len = tvb_get_letohl(tvb, offset);
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_string_length, tvb, offset, 4, ENC_LITTLE_ENDIAN);
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_string, tvb, offset+4, str_len, ENC_UTF_8);
        offset += str_len;
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_db_ptr, tvb, offset, 12, ENC_NA);
        offset += 12;
        break;
      case BSON_ELEMENT_TYPE_JS_CODE_SCOPE:
        /* code_w_s ::= int32 string document */
        proto_tree_add_item(element_sub_tree, hf_mongo_element_length, tvb, offset, 4, ENC_LITTLE_ENDIAN);
        e_len = tvb_get_letohl(tvb, offset);
        offset += 4;
        str_len = tvb_get_letohl(tvb, offset);
        js_code = proto_tree_add_item(element_sub_tree, hf_mongo_element_value_js_code, tvb, offset, str_len+4, ENC_NA);
        js_code_sub_tree = proto_item_add_subtree(js_code, ett_mongo_code);
        proto_tree_add_item(js_code_sub_tree, hf_mongo_element_value_string_length, tvb, offset, 4, ENC_LITTLE_ENDIAN);
        proto_tree_add_item(js_code_sub_tree, hf_mongo_element_value_string, tvb, offset+4, str_len, ENC_UTF_8);
        offset += str_len+4;
        doc_len = e_len - (str_len + 8);
        js_scope = proto_tree_add_item(element_sub_tree, hf_mongo_element_value_js_scope, tvb, offset, doc_len, ENC_NA);
        js_scope_sub_tree = proto_item_add_subtree(js_scope, ett_mongo_code);
        offset += dissect_bson_document(tvb, pinfo, offset, js_scope_sub_tree, hf_mongo_document);
        break;
      case BSON_ELEMENT_TYPE_INT32:
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_int32, tvb, offset, 4, ENC_LITTLE_ENDIAN);
        offset += 4;
        break;
      case BSON_ELEMENT_TYPE_DATETIME:
      case BSON_ELEMENT_TYPE_TIMESTAMP:
        /* TODO Implement routine to convert datetime & timestamp values to UTC date/time */
        /* for now, simply display the integer value */
      case BSON_ELEMENT_TYPE_INT64:
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_int64, tvb, offset, 8, ENC_LITTLE_ENDIAN);
        offset += 8;
        break;
      case BSON_ELEMENT_TYPE_DECIMAL128:
        /* TODO Implement routine to convert to decimal128 for now, simply display bytes */
        /* https://github.com/mongodb/specifications/blob/master/source/bson-decimal128/decimal128.rst */
        proto_tree_add_item(element_sub_tree, hf_mongo_element_value_decimal128, tvb, offset, 16, ENC_NA);
        offset += 16;
        break;
      default:
        break;
    }  /* end switch() */
  } while (offset < final_offset-1);

  // Restore depth.
  nest_level--;
  p_set_proto_depth(pinfo, proto_mongo, nest_level);

  return document_length;
}

/* get_first_bson_field returns the first field of the BSON document. Returned string is NULL terminated. Returns NULL on error. */
static uint8_t* get_first_bson_field(tvbuff_t *tvb, packet_info *pinfo, unsigned offset)
{
  int32_t document_length = tvb_get_letohl(tvb, offset);

  if (document_length < 5) {
    return NULL;
  }

  if (document_length > BSON_MAX_DOC_SIZE) {
    return NULL;
  }

  if (document_length == 5) {
    /* Empty document. */
    return NULL;
  }

  offset += 4;

  /* Read first document element. Ignore first byte (type) */
  return tvb_get_stringz_enc(pinfo->pool, tvb, offset+1, NULL /* out length */, ENC_ASCII);
}

static int
dissect_mongo_reply(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree)
{
  proto_item *ti;
  proto_tree *flags_tree;
  int i, number_returned;

  ti = proto_tree_add_item(tree, hf_mongo_reply_flags, tvb, offset, 4, ENC_NA);
  flags_tree = proto_item_add_subtree(ti, ett_mongo_flags);
  proto_tree_add_item(flags_tree, hf_mongo_reply_flags_cursornotfound, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_reply_flags_queryfailure, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_reply_flags_sharedconfigstale, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_reply_flags_awaitcapable, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset += 4;

  proto_tree_add_item(tree, hf_mongo_cursor_id, tvb, offset, 8, ENC_LITTLE_ENDIAN);
  offset += 8;

  proto_tree_add_item(tree, hf_mongo_starting_from, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset += 4;

  proto_tree_add_item(tree, hf_mongo_number_returned, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  number_returned = tvb_get_letohl(tvb, offset);
  offset += 4;

  for (i=0; i < number_returned; i++)
  {
    offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_document);
  }
  return offset;
}

static int
dissect_mongo_msg(tvbuff_t *tvb, unsigned offset, proto_tree *tree)
{
  proto_tree_add_item(tree, hf_mongo_message, tvb, offset, -1, ENC_ASCII);
  offset += tvb_strsize(tvb, offset);

  return offset;
}

static int
dissect_mongo_update(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree)
{
  proto_item *ti;
  proto_tree *flags_tree;

  proto_tree_add_item(tree, hf_mongo_zero, tvb, offset, 4, ENC_NA);
  offset += 4;

  offset += dissect_fullcollectionname(tvb, offset, tree);

  ti = proto_tree_add_item(tree, hf_mongo_update_flags, tvb, offset, 4, ENC_NA);
  flags_tree = proto_item_add_subtree(ti, ett_mongo_flags);
  proto_tree_add_item(flags_tree, hf_mongo_update_flags_upsert, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_update_flags_multiupdate, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset += 4;

  offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_selector);

  offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_update);

  return offset;
}

static int
dissect_mongo_insert(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree)
{
  proto_item *ti;
  proto_tree *flags_tree;

  ti = proto_tree_add_item(tree, hf_mongo_insert_flags, tvb, offset, 4, ENC_NA);
  flags_tree = proto_item_add_subtree(ti, ett_mongo_flags);
  proto_tree_add_item(flags_tree, hf_mongo_insert_flags_continueonerror, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset += 4;

  offset += dissect_fullcollectionname(tvb, offset, tree);

  while(offset < tvb_reported_length(tvb)) {
    offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_document);
  }

  return offset;
}

static int
dissect_mongo_query(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree, uint8_t **command_name)
{
  proto_item *ti;
  proto_tree *flags_tree;
  int fullcollectionname_len;
  bool is_command = false;

  ti = proto_tree_add_item(tree, hf_mongo_query_flags, tvb, offset, 4, ENC_NA);
  flags_tree = proto_item_add_subtree(ti, ett_mongo_flags);
  proto_tree_add_item(flags_tree, hf_mongo_query_flags_tailablecursor, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_query_flags_slaveok, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_query_flags_oplogreplay, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_query_flags_nocursortimeout, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_query_flags_awaitdata, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_query_flags_exhaust, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(flags_tree, hf_mongo_query_flags_partial, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset += 4;

  fullcollectionname_len = dissect_fullcollectionname(tvb, offset, tree);
  if (tvb_strneql (tvb, offset, "admin.$cmd", strlen("admin.$cmd") + 1) == 0) {
    is_command = true;
  }
  offset += fullcollectionname_len;

  proto_tree_add_item(tree, hf_mongo_number_to_skip, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset += 4;

  proto_tree_add_item(tree, hf_mongo_number_to_return, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset +=4;

  if (is_command && command_name && *command_name == NULL) {
    *command_name = get_first_bson_field (tvb, pinfo, offset);
  }

  offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_query);

  while(offset < tvb_reported_length(tvb)) {
    offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_return_field_selector);
  }
  return offset;
}

static int
dissect_mongo_getmore(tvbuff_t *tvb, unsigned offset, proto_tree *tree)
{

  proto_tree_add_item(tree, hf_mongo_zero, tvb, offset, 4, ENC_NA);
  offset += 4;

  offset += dissect_fullcollectionname(tvb, offset, tree);

  proto_tree_add_item(tree, hf_mongo_number_to_return, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset += 4;

  proto_tree_add_item(tree, hf_mongo_cursor_id, tvb, offset, 8, ENC_LITTLE_ENDIAN);
  offset += 8;

  return offset;
}

static int
dissect_mongo_delete(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree)
{
  proto_item *ti;
  proto_tree *flags_tree;

  proto_tree_add_item(tree, hf_mongo_zero, tvb, offset, 4, ENC_NA);
  offset += 4;

  offset += dissect_fullcollectionname(tvb, offset, tree);

  ti = proto_tree_add_item(tree, hf_mongo_delete_flags, tvb, offset, 4, ENC_NA);
  flags_tree = proto_item_add_subtree(ti, ett_mongo_flags);
  proto_tree_add_item(flags_tree, hf_mongo_delete_flags_singleremove, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset += 4;

  offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_selector);

  return offset;
}

static int
dissect_mongo_kill_cursors(tvbuff_t *tvb, unsigned offset, proto_tree *tree)
{

  proto_tree_add_item(tree, hf_mongo_zero, tvb, offset, 4, ENC_NA);
  offset += 4;

  proto_tree_add_item(tree, hf_mongo_number_of_cursor_ids, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  offset += 4;

  while(offset < tvb_reported_length(tvb)) {
    proto_tree_add_item(tree, hf_mongo_cursor_id, tvb, offset, 8, ENC_LITTLE_ENDIAN);
    offset +=8;
  }
  return offset;
}

static int
dissect_mongo_op_command(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree)
{
  int32_t db_length, cmd_length;

  db_length = tvb_strsize(tvb, offset);
  proto_tree_add_item(tree, hf_mongo_database, tvb, offset, db_length, ENC_ASCII);
  offset += db_length;

  cmd_length = tvb_strsize(tvb, offset);
  proto_tree_add_item(tree, hf_mongo_commandname, tvb, offset, cmd_length, ENC_ASCII);
  offset += cmd_length;

  offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_metadata);

  offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_commandargs);

  return offset;
}

static int
dissect_mongo_op_commandreply(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree)
{

  offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_metadata);

  offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_commandreply);

  if (tvb_reported_length_remaining(tvb, offset) > 0){
    offset += dissect_bson_document(tvb, pinfo, offset, tree, hf_mongo_outputdocs);
  }

  return offset;
}

static int
// NOLINTNEXTLINE(misc-no-recursion)
dissect_mongo_op_compressed(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree, unsigned *effective_opcode, uint8_t **command_name)
{
  unsigned opcode = 0;
  uint8_t compressor;
  proto_item *ti;
  proto_tree *compression_info_tree;

  ti = proto_tree_add_item(tree, hf_mongo_compression_info, tvb, offset, 9, ENC_NA);
  compression_info_tree = proto_item_add_subtree(ti, ett_mongo_compression_info);
  proto_tree_add_item(compression_info_tree, hf_mongo_original_op_code, tvb, offset, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(compression_info_tree, hf_mongo_uncompressed_size, tvb, offset + 4, 4, ENC_LITTLE_ENDIAN);
  proto_tree_add_item(compression_info_tree, hf_mongo_compressor, tvb, offset + 8, 1, ENC_NA);
  proto_tree_add_item(compression_info_tree, hf_mongo_compressed_data, tvb, offset + 9, -1, ENC_NA);

  opcode = tvb_get_letohl(tvb, offset);
  *effective_opcode = opcode;
  compressor = tvb_get_uint8(tvb, offset + 8);
  offset += 9;

  switch(compressor) {
  case MONGO_COMPRESSOR_NOOP:
    offset = dissect_opcode_types(tvb, pinfo, offset, tree, opcode, effective_opcode, command_name);
    break;

#ifdef HAVE_SNAPPY
  case MONGO_COMPRESSOR_SNAPPY: {
    tvbuff_t* uncompressed_tvb = tvb_child_uncompress_snappy(tvb, tvb, offset, tvb_captured_length_remaining(tvb, offset));
    if (uncompressed_tvb) {
        add_new_data_source(pinfo, uncompressed_tvb, "Decompressed Data");

        dissect_opcode_types(uncompressed_tvb, pinfo, 0, tree, opcode, effective_opcode, command_name);
    } else {
      expert_add_info_format(pinfo, ti, &ei_mongo_unsupported_compression, "Error uncompressing snappy data");
    }

    offset = tvb_reported_length(tvb);
  } break;
#endif

#ifdef HAVE_ZSTD
  case MONGO_COMPRESSOR_ZSTD:
  {
    tvbuff_t *uncompressed_tvb = tvb_child_uncompress_zstd (tvb, tvb, offset, tvb_captured_length_remaining (tvb, offset));
    if (!uncompressed_tvb) {
      expert_add_info_format(pinfo, ti, &ei_mongo_unsupported_compression, "Error uncompressing zstd data");
    } else {
      add_new_data_source(pinfo, uncompressed_tvb, "Decompressed Data");
      dissect_opcode_types(uncompressed_tvb, pinfo, 0, tree, opcode, effective_opcode, command_name);
    }

    offset = tvb_reported_length(tvb);
  }
  break;
#endif

  case MONGO_COMPRESSOR_ZLIB: {
    tvbuff_t* compressed_tvb = tvb_child_uncompress_zlib(tvb, tvb, offset, tvb_captured_length_remaining(tvb, offset));

    if (compressed_tvb) {
      add_new_data_source(pinfo, compressed_tvb, "Decompressed Data");

      dissect_opcode_types(compressed_tvb, pinfo, 0, tree, opcode, effective_opcode, command_name);
    } else {
      proto_tree_add_item(compression_info_tree, hf_mongo_unsupported_compressed, tvb, offset, -1, ENC_NA);
      expert_add_info_format(pinfo, ti, &ei_mongo_unsupported_compression, "Error uncompressing zlib data");
    }

    offset = tvb_reported_length(tvb);
  } break;

  default:
    proto_tree_add_item(compression_info_tree, hf_mongo_unsupported_compressed, tvb, offset, -1, ENC_NA);
    expert_add_info_format(pinfo, ti, &ei_mongo_unsupported_compression, "Unsupported compression format: %d", compressor);
    offset = tvb_reported_length(tvb);
    break;
  }

  return offset;
}

static int
dissect_op_msg_section(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree, uint8_t **command_name)
{
  proto_item *ti;
  proto_tree *section_tree;
  uint8_t e_type;
  int section_len = -1;   /* Section length */

  e_type = tvb_get_uint8(tvb, offset);

  ti = proto_tree_add_item(tree, hf_mongo_msg_sections_section, tvb, offset, 1, ENC_NA);
  section_tree = proto_item_add_subtree(ti, ett_mongo_section);
  proto_tree_add_item(section_tree, hf_mongo_msg_sections_section_kind, tvb, offset, 1, ENC_LITTLE_ENDIAN);
  offset += 1;

  section_len = tvb_get_letohil(tvb, offset);
  /* The section length must be strictly smaller than the total message size,
   * both signed int32s. This prevents signed integer overflow. */
  if (section_len < 0 || section_len == INT32_MAX) {
    proto_tree_add_expert_format(section_tree, pinfo, &ei_mongo_section_size_bad, tvb, offset, 4, "Bogus Mongo message section size: %i", section_len);
    THROW(ReportedBoundsError);
  }
  proto_item_set_len(ti, 1 + section_len);

  switch (e_type) {
    case KIND_BODY:
      section_len = dissect_bson_document(tvb, pinfo, offset, section_tree, hf_mongo_msg_sections_section_body);
      /* If section_len is bogus (e.g., negative), dissect_bson_document sets
       * an expert info and can return a different value than read above.
       */
      if (command_name && *command_name == NULL) {
        *command_name = get_first_bson_field (tvb, pinfo, offset);
      }
      break;
    case KIND_DOCUMENT_SEQUENCE: {
      int32_t dsi_length;
      int32_t to_read = section_len;
      proto_item *documents;
      proto_tree *documents_tree;

      proto_tree_add_item(section_tree, hf_mongo_msg_sections_section_size, tvb, offset, 4, ENC_LITTLE_ENDIAN);
      /* This is redundant with the lengths in the documents, we don't use this
       * size at all. We could still report an expert info if it's bogus.
       */
      offset += 4;
      to_read -= 4;

      dsi_length = tvb_strsize(tvb, offset);
      proto_tree_add_item(section_tree, hf_mongo_msg_sections_section_doc_sequence_id, tvb, offset, dsi_length, ENC_ASCII);
      offset += dsi_length;
      to_read -= dsi_length;

      documents = proto_tree_add_item(section_tree, hf_mongo_msg_sections_section_doc_sequence, tvb, offset, to_read, ENC_NA);
      documents_tree = proto_item_add_subtree(documents, ett_mongo_doc_sequence);

      while (to_read > 0){
        int32_t doc_size = dissect_bson_document(tvb, pinfo, offset, documents_tree, hf_mongo_document);
        to_read -= doc_size;
        offset += doc_size;
      }

    } break;
    default:
      expert_add_info_format(pinfo, tree, &ei_mongo_unknown, "Unknown section type: %u", e_type);
  }

  return 1 + section_len;
}

static int
dissect_mongo_op_msg(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *tree, uint8_t **command_name)
{
  static int * const mongo_msg_flags[] = {
    &hf_mongo_msg_flags_checksumpresent,
    &hf_mongo_msg_flags_moretocome,
    &hf_mongo_msg_flags_exhaustallowed,
    NULL
  };
  uint64_t op_msg_flags;
  bool checksum_present = false;

  proto_tree_add_bitmask_ret_uint64 (tree, tvb, offset, hf_mongo_msg_flags, ett_mongo_msg_flags, mongo_msg_flags, ENC_LITTLE_ENDIAN, &op_msg_flags);
  if (op_msg_flags & 0x00000001) {
    checksum_present = true;
  }

  offset += 4;

  while (tvb_reported_length_remaining(tvb, offset) > (checksum_present ? 4 : 0)){
    offset += dissect_op_msg_section(tvb, pinfo, offset, tree, command_name);
  }

  if (checksum_present) {
    uint32_t calculated_checksum = ~crc32c_tvb_offset_calculate (tvb, 0, tvb_reported_length (tvb) - 4, CRC32C_PRELOAD);
    proto_tree_add_checksum(tree, tvb, offset, hf_mongo_msg_checksum, hf_mongo_msg_checksum_status, &ei_mongo_msg_checksum, pinfo, calculated_checksum, ENC_BIG_ENDIAN, PROTO_CHECKSUM_VERIFY);
    offset += 4;
  }

  return offset;
}

static int
// NOLINTNEXTLINE(misc-no-recursion)
dissect_opcode_types(tvbuff_t *tvb, packet_info *pinfo, unsigned offset, proto_tree *mongo_tree, unsigned opcode, unsigned *effective_opcode, uint8_t **command_name)
{
    *effective_opcode = opcode;

    unsigned recursion_depth = p_get_proto_depth(pinfo, proto_mongo);
    DISSECTOR_ASSERT(recursion_depth <= BSON_MAX_NESTING);
    p_set_proto_depth(pinfo, proto_mongo, recursion_depth + 1);

    switch(opcode){
    case OP_REPLY:
      offset = dissect_mongo_reply(tvb, pinfo, offset, mongo_tree);
      break;
    case OP_MESSAGE:
      offset = dissect_mongo_msg(tvb, offset, mongo_tree);
      break;
    case OP_UPDATE:
      offset = dissect_mongo_update(tvb, pinfo, offset, mongo_tree);
      break;
    case OP_INSERT:
      offset = dissect_mongo_insert(tvb, pinfo, offset, mongo_tree);
      break;
    case OP_QUERY:
      offset = dissect_mongo_query(tvb, pinfo, offset, mongo_tree, command_name);
      break;
    case OP_GET_MORE:
      offset = dissect_mongo_getmore(tvb, offset, mongo_tree);
      break;
    case OP_DELETE:
      offset = dissect_mongo_delete(tvb, pinfo, offset, mongo_tree);
      break;
    case OP_KILL_CURSORS:
      offset = dissect_mongo_kill_cursors(tvb, offset, mongo_tree);
      break;
    case OP_COMMAND:
      offset = dissect_mongo_op_command(tvb, pinfo, offset, mongo_tree);
      break;
    case OP_COMMANDREPLY:
      offset = dissect_mongo_op_commandreply(tvb, pinfo, offset, mongo_tree);
      break;
    case OP_COMPRESSED:
      offset = dissect_mongo_op_compressed(tvb, pinfo, offset, mongo_tree, effective_opcode, command_name);
      break;
    case OP_MSG:
      offset = dissect_mongo_op_msg(tvb, pinfo, offset, mongo_tree, command_name);
      break;
    default:
      /* No default Action */
      break;
    }

    p_set_proto_depth(pinfo, proto_mongo, recursion_depth);

    return offset;
}

static int
dissect_mongo_pdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
{
    proto_item *ti;
    proto_tree *mongo_tree;
    unsigned offset = 0, opcode, effective_opcode = 0;
    uint32_t response_to;
    uint8_t *command_name = NULL;

    col_set_str(pinfo->cinfo, COL_PROTOCOL, "MONGO");

    ti = proto_tree_add_item(tree, proto_mongo, tvb, 0, -1, ENC_NA);

    mongo_tree = proto_item_add_subtree(ti, ett_mongo);

    proto_tree_add_item(mongo_tree, hf_mongo_message_length, tvb, offset, 4, ENC_LITTLE_ENDIAN);
    offset += 4;

    proto_tree_add_item(mongo_tree, hf_mongo_request_id, tvb, offset, 4, ENC_LITTLE_ENDIAN);
    offset += 4;

    proto_tree_add_item_ret_uint(mongo_tree, hf_mongo_response_to, tvb, offset, 4, ENC_LITTLE_ENDIAN, &response_to);
    offset += 4;

    proto_tree_add_item(mongo_tree, hf_mongo_op_code, tvb, offset, 4, ENC_LITTLE_ENDIAN);
    opcode = tvb_get_letohl(tvb, offset);
    offset += 4;

    offset = dissect_opcode_types(tvb, pinfo, offset, mongo_tree, opcode, &effective_opcode, &command_name);

    if (opcode == 1 || response_to != 0)
    {
      col_set_str(pinfo->cinfo, COL_INFO, "Response :");
    }
    else
    {
      col_set_str(pinfo->cinfo, COL_INFO, "Request :");

    }
    col_append_fstr(pinfo->cinfo, COL_INFO, " %s", val_to_str_const(effective_opcode, opcode_vals, "Unknown"));

    if(opcode != effective_opcode) {
      col_append_str(pinfo->cinfo, COL_INFO, " (Compressed)");
    }

    if (opcode != 1 && response_to == 0 && command_name) {
      col_append_fstr(pinfo->cinfo, COL_INFO, " (%s)", (char*) command_name);
    }

    if(offset < tvb_reported_length(tvb))
    {
      ti = proto_tree_add_item(mongo_tree, hf_mongo_unknown, tvb, offset, -1, ENC_NA);
      expert_add_info(pinfo, ti, &ei_mongo_unknown);
    }

    return tvb_captured_length(tvb);
}
static unsigned
get_mongo_pdu_len(packet_info *pinfo _U_, tvbuff_t *tvb, int offset, void *data _U_)
{
  uint32_t plen;

  /*
  * Get the length of the MONGO packet.
  */
  plen = tvb_get_letohl(tvb, offset);
  /* XXX - This is signed, but we can only return an unsigned to
   * tcp_dissect_pdus. If negative, should we return something like
   * 1 (less than the fixed len 4) so that it causes a ReportedBoundsError?
   */

  return plen;
}

static int
dissect_mongo(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data)
{
  tcp_dissect_pdus(tvb, pinfo, tree, 1, 4, get_mongo_pdu_len, dissect_mongo_pdu, data);
  return tvb_captured_length(tvb);
}

static bool
test_mongo(packet_info *pinfo _U_, tvbuff_t *tvb, int offset, void *data _U_)
{
  uint32_t opcode;

  if (tvb_captured_length_remaining(tvb, offset) < 16) {
    return false;
  }

  if (tvb_get_letohil(tvb, offset) < 4) {
    /* Message sizes are signed in the MongoDB Wire Protocol and
     * include the header.
     */
    return false;
  }

  opcode = tvb_get_letohl(tvb, offset + 12);
  /* As 5.1 and later uses only 2 opcodes, we might be able to use that
   * (plus some other information) to do heuristics on other ports.
   */
  return (try_val_to_str(opcode, opcode_vals) != NULL);
}

static int
dissect_mongo_tcp_heur(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data)
{
  if (!test_mongo(pinfo, tvb, 0, data)) {
    return 0;
    /* The TLS heuristic dissector should catch this if over TLS. */
  }
  conversation_t *conversation = find_or_create_conversation(pinfo);
  conversation_set_dissector(conversation, mongo_handle);

  return dissect_mongo(tvb, pinfo, tree, data);
}

void
proto_register_mongo(void)
{
  expert_module_t* expert_mongo;

  static hf_register_info hf[] = {
    { &hf_mongo_message_length,
      { "Message Length", "mongo.message_length",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Total message size (including header)", HFILL }
    },
    { &hf_mongo_request_id,
      { "Request ID", "mongo.request_id",
      FT_UINT32, BASE_HEX_DEC, NULL, 0x0,
      "Identifier for this message", HFILL }
    },
    { &hf_mongo_response_to,
      { "Response To", "mongo.response_to",
      FT_UINT32, BASE_HEX_DEC, NULL, 0x0,
      "RequestID from the original request", HFILL }
    },
    { &hf_mongo_op_code,
      { "OpCode", "mongo.opcode",
      FT_INT32, BASE_DEC, VALS(opcode_vals), 0x0,
      "Type of request message", HFILL }
    },
    { &hf_mongo_query_flags,
      { "Query Flags", "mongo.query.flags",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Bit vector of query options.", HFILL }
    },
    { &hf_mongo_fullcollectionname,
      { "fullCollectionName", "mongo.full_collection_name",
      FT_STRINGZ, BASE_NONE, NULL, 0x0,
      "The full collection name is the concatenation of the database name with the"
        " collection name, using a dot for the concatenation", HFILL }
    },
    { &hf_mongo_database_name,
      { "Database Name", "mongo.database_name",
      FT_STRING, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_collection_name,
      { "Collection Name", "mongo.collection_name",
      FT_STRING, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_reply_flags,
      { "Reply Flags", "mongo.reply.flags",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Bit vector of reply options.", HFILL }
    },
    { &hf_mongo_reply_flags_cursornotfound,
      { "Cursor Not Found", "mongo.reply.flags.cursornotfound",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000001,
      "Set when getMore is called but the cursor id is not valid at the server", HFILL }
    },
    { &hf_mongo_reply_flags_queryfailure,
      { "Query Failure", "mongo.reply.flags.queryfailure",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000002,
      "Set when query failed. Results consist of one document containing an $err"
        " field describing the failure.", HFILL }
    },
    { &hf_mongo_reply_flags_sharedconfigstale,
      { "Shared Config Stale", "mongo.reply.flags.sharedconfigstale",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000004,
      NULL, HFILL }
    },
    { &hf_mongo_reply_flags_awaitcapable,
      { "Await Capable", "mongo.reply.flags.awaitcapable",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000008,
      "Set when the server supports the AwaitData Query option", HFILL }
    },
    { &hf_mongo_message,
      { "Message", "mongo.message",
      FT_STRINGZ, BASE_NONE, NULL, 0x0,
      "Message for the database", HFILL }
    },
    { &hf_mongo_cursor_id,
      { "Cursor ID", "mongo.cursor_id",
      FT_INT64, BASE_DEC, NULL, 0x0,
      "Cursor id if client needs to do get more's", HFILL }
    },
    { &hf_mongo_starting_from,
      { "Starting From", "mongo.starting_from",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Where in the cursor this reply is starting", HFILL }
    },
    { &hf_mongo_number_returned,
      { "Number Returned", "mongo.number_returned",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Number of documents in the reply", HFILL }
    },
    { &hf_mongo_document,
      { "Document", "mongo.document",
      FT_NONE, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_document_length,
      { "Document length", "mongo.document.length",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Length of BSON Document", HFILL }
    },
    { &hf_mongo_document_empty,
      { "Empty Document", "mongo.document.empty",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Document with no elements", HFILL }
    },
    { &hf_mongo_zero,
      { "Zero", "mongo.document.zero",
      FT_BYTES, BASE_NONE, NULL, 0x0,
      "Reserved (Must be is Zero)", HFILL }
    },
    { &hf_mongo_update_flags,
      { "Update Flags", "mongo.update.flags",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Bit vector of update options.", HFILL }
    },
    { &hf_mongo_update_flags_upsert,
      { "Upsert", "mongo.update.flags.upsert",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000001,
      "If set, the database will insert the supplied object into the collection if no"
        " matching document is found", HFILL }
    },
    { &hf_mongo_update_flags_multiupdate,
      { "Multi Update", "mongo.update.flags.multiupdate",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000002,
      "If set, the database will update all matching objects in the collection."
        " Otherwise only updates first matching doc.", HFILL }
    },
    { &hf_mongo_selector,
      { "Selector", "mongo.selector",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "The query to select the document", HFILL }
    },
    { &hf_mongo_update,
      { "Update", "mongo.update",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Specification of the update to perform", HFILL }
    },
    { &hf_mongo_insert_flags,
      { "Insert Flags", "mongo.insert.flags",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Bit vector of insert options.", HFILL }
    },
    { &hf_mongo_insert_flags_continueonerror,
      { "ContinueOnError", "mongo.insert.flags.continueonerror",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000001,
      "If set, the database will not stop processing a bulk insert if one fails"
        " (eg due to duplicate IDs)", HFILL }
    },
    { &hf_mongo_query_flags_tailablecursor,
      { "Tailable Cursor", "mongo.query.flags.tailable_cursor",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000002,
      "Tailable means cursor is not closed when the last data is retrieved", HFILL }
    },
    { &hf_mongo_query_flags_slaveok,
      { "Slave OK", "mongo.query.flags.slave_ok",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000004,
      "Allow query of replica slave", HFILL }
    },
    { &hf_mongo_query_flags_oplogreplay,
      { "Op Log Reply", "mongo.query.flags.op_log_reply",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000008,
      "Internal replication use only", HFILL }
    },
    { &hf_mongo_query_flags_nocursortimeout,
      { "No Cursor Timeout", "mongo.query.flags.no_cursor_timeout",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000010,
      "The server normally times out idle cursors after an inactivity period (10 minutes)"
        " to prevent excess memory use. Set this option to prevent that", HFILL }
    },
    { &hf_mongo_query_flags_awaitdata,
      { "AwaitData", "mongo.query.flags.awaitdata",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000020,
      "If we are at the end of the data, block for a while rather than returning no data."
        " After a timeout period, we do return as normal", HFILL }
    },
    { &hf_mongo_query_flags_exhaust,
      { "Exhaust", "mongo.query.flags.exhaust",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000040,
      "Stream the data down full blast in multiple more packages, on the assumption"
        " that the client will fully read all data queried", HFILL }
    },
    { &hf_mongo_query_flags_partial,
      { "Partial", "mongo.query.flags.partial",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000080,
      "Get partial results from a mongos if some shards are down (instead of throwing an error)", HFILL }
    },
    { &hf_mongo_number_to_skip,
      { "Number To Skip", "mongo.number_to_skip",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Number of documents in the skip", HFILL }
    },
    { &hf_mongo_number_to_return,
      { "Number to Return", "mongo.number_to_return",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Number of documents in the return", HFILL }
    },
    { &hf_mongo_query,
      { "Query", "mongo.query",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Query BSON Document", HFILL }
    },
    { &hf_mongo_return_field_selector,
      { "Return Field Selector", "mongo.return_field_selector",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Return Field Selector BSON Document", HFILL }
    },
    { &hf_mongo_delete_flags,
      { "Delete Flags", "mongo.delete.flags",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Bit vector of delete options.", HFILL }
    },
    { &hf_mongo_delete_flags_singleremove,
      { "Single Remove", "mongo.delete.flags.singleremove",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000001,
      "If set, the database will remove only the first matching document in the"
        " collection. Otherwise all matching documents will be removed", HFILL }
    },
    { &hf_mongo_compression_info,
      { "Compression Info", "mongo.compression",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Compressed Packet", HFILL }
    },
    { &hf_mongo_original_op_code,
      { "Original OpCode", "mongo.compression.original_opcode",
      FT_INT32, BASE_DEC, VALS(opcode_vals), 0x0,
      "Type of request message (Wrapped)", HFILL }
    },
    { &hf_mongo_uncompressed_size,
      { "Uncompressed Size", "mongo.compression.original_size",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Size of the uncompressed packet", HFILL }
    },
    { &hf_mongo_compressor,
      { "Compressor", "mongo.compression.compressor",
      FT_INT8, BASE_DEC, VALS(compressor_vals), 0x0,
      "Compression engine", HFILL }
    },
    { &hf_mongo_compressed_data,
      { "Compressed Data", "mongo.compression.compressed_data",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "The compressed data", HFILL }
    },
    { &hf_mongo_unsupported_compressed,
      { "Unsupported Compressed Data", "mongo.compression.unsupported_compressed",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "This data is compressed with an unsupported compressor engine", HFILL }
    },
    { &hf_mongo_msg_flags,
      { "Message Flags", "mongo.msg.flags",
      FT_UINT32, BASE_HEX, NULL, 0x0,
      "Bit vector of msg options.", HFILL }
    },
    { &hf_mongo_msg_flags_checksumpresent,
      { "ChecksumPresent", "mongo.msg.flags.checksumpresent",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000001,
      "The message ends with 4 bytes containing a CRC-32C [1] checksum", HFILL }
    },
    { &hf_mongo_msg_flags_moretocome,
      { "MoreToCome", "mongo.msg.flags.moretocome",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00000002,
      "Another message will follow this one without further action from the receiver", HFILL }
    },
    { &hf_mongo_msg_flags_exhaustallowed,
      { "ExhaustAllowed", "mongo.msg.flags.exhaustallowed",
      FT_BOOLEAN, 32, TFS(&tfs_yes_no), 0x00010000,
      "The client is prepared for multiple replies to this request using the moreToCome bit.", HFILL }
    },
    { &hf_mongo_msg_sections_section,
      { "Section", "mongo.msg.sections.section",
      FT_NONE, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_msg_sections_section_kind,
      { "Kind", "mongo.msg.sections.section.kind",
      FT_INT32, BASE_DEC, VALS(section_kind_vals), 0x0,
      "Type of section", HFILL }
    },
    { &hf_mongo_msg_sections_section_body,
      { "BodyDocument", "mongo.msg.sections.section.body",
      FT_NONE, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_msg_sections_section_doc_sequence,
      { "DocumentSequence", "mongo.msg.sections.section.doc_sequence",
      FT_NONE, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_msg_sections_section_size,
      { "Size", "mongo.msg.sections.section.size",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Size (in bytes) of document sequence", HFILL }
    },
    { &hf_mongo_msg_sections_section_doc_sequence_id,
      { "SeqID", "mongo.msg.sections.section.doc_sequence_id",
      FT_STRING, BASE_NONE, NULL, 0x0,
      "Document sequence identifier", HFILL }
    },
    { &hf_mongo_msg_checksum,
      { "Checksum", "mongo.msg.checksum",
      FT_UINT32, BASE_HEX, NULL, 0x0,
      "CRC32C checksum.", HFILL }
    },
    { &hf_mongo_msg_checksum_status,
      { "Checksum Status", "mongo.msg.checksum.status",
      FT_UINT8, BASE_NONE, VALS(proto_checksum_vals), 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_number_of_cursor_ids,
      { "Number of Cursor IDS", "mongo.number_to_cursor_ids",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Number of cursorIDs in message", HFILL }
    },
    { &hf_mongo_elements,
      { "Elements", "mongo.elements",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Document Elements", HFILL }
    },
    { &hf_mongo_element_name,
      { "Element", "mongo.element.name",
      FT_STRING, BASE_NONE, NULL, 0x0,
      "Element Name", HFILL }
    },
    { &hf_mongo_element_type,
      { "Type", "mongo.element.type",
      FT_UINT8, BASE_HEX_DEC, VALS(element_type_vals), 0x0,
      "Element Type", HFILL }
    },
    { &hf_mongo_element_length,
      { "Length", "mongo.element.length",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Element Length", HFILL }
    },
    { &hf_mongo_element_value_boolean,
      { "Value", "mongo.element.value.bool",
      FT_BOOLEAN, BASE_NONE, NULL, 0x0,
      "Element Value", HFILL }
    },
    { &hf_mongo_element_value_int32,
      { "Value", "mongo.element.value.int",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Element Value", HFILL }
    },
    { &hf_mongo_element_value_int64,
      { "Value", "mongo.element.value.int64",
      FT_INT64, BASE_DEC, NULL, 0x0,
      "Element Value", HFILL }
    },
    { &hf_mongo_element_value_decimal128,
      { "Value", "mongo.element.value.decimal128",
      FT_BYTES, BASE_NONE, NULL, 0x0,
      "Element Value", HFILL }
    },
    { &hf_mongo_element_value_double,
      { "Value", "mongo.element.value.double",
      FT_DOUBLE, BASE_NONE, NULL, 0x0,
      "Element Value", HFILL }
    },
    { &hf_mongo_element_value_string,
      { "Value", "mongo.element.value.string",
      FT_STRING, BASE_NONE, NULL, 0x0,
      "Element Value", HFILL }
    },
    { &hf_mongo_element_value_string_length,
      { "Length", "mongo.element.value.length",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Element Value Length", HFILL }
    },
    { &hf_mongo_element_value_binary,
      { "Value", "mongo.element.value.bytes",
      FT_BYTES, BASE_NONE, NULL, 0x0,
      "Element Value", HFILL }
    },
    { &hf_mongo_element_value_binary_length,
      { "Length", "mongo.element.value.length",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "Binary Element Length", HFILL }
    },
    { &hf_mongo_element_value_regex_pattern,
      { "Value", "mongo.element.value.regex.pattern",
      FT_STRING, BASE_NONE, NULL, 0x0,
      "Regex Pattern", HFILL }
    },
    { &hf_mongo_element_value_regex_options,
      { "Value", "mongo.element.value.regex.options",
      FT_STRING, BASE_NONE, NULL, 0x0,
      "Regex Options", HFILL }
    },
    { &hf_mongo_element_value_objectid,
      { "ObjectID", "mongo.element.value.objectid",
      FT_BYTES, BASE_NONE, NULL, 0x0,
      "ObjectID Value", HFILL }
    },
    { &hf_mongo_element_value_objectid_time,
      { "ObjectID Time", "mongo.element.value.objectid.time",
      FT_INT32, BASE_DEC, NULL, 0x0,
      "ObjectID timestampt", HFILL }
    },
    { &hf_mongo_element_value_objectid_host,
      { "ObjectID Host", "mongo.element.value.objectid.host",
      FT_UINT24, BASE_HEX, NULL, 0x0,
      "ObjectID Host Hash", HFILL }
    },
    { &hf_mongo_element_value_objectid_machine_id,
      { "ObjectID Machine", "mongo.element.value.objectid.machine_id",
      FT_BYTES, BASE_NONE, NULL, 0x0,
      "ObjectID machine ID", HFILL }
    },
    { &hf_mongo_element_value_objectid_pid,
      { "ObjectID PID", "mongo.element.value.objectid.pid",
      FT_UINT16, BASE_DEC, NULL, 0x0,
      "ObjectID process ID", HFILL }
    },
    { &hf_mongo_element_value_objectid_inc,
      { "ObjectID Inc", "mongo.element.value.objectid.inc",
      FT_UINT24, BASE_DEC, NULL, 0x0,
      "ObjectID increment", HFILL }
    },
    { &hf_mongo_element_value_db_ptr,
      { "ObjectID", "mongo.element.value.db_ptr",
      FT_BYTES, BASE_NONE, NULL, 0x0,
      "DBPointer", HFILL }
    },
    { &hf_mongo_element_value_js_code,
      { "JavaScript code", "mongo.element.value.js_code",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "JavaScript code to be evaluated", HFILL }
    },
    { &hf_mongo_element_value_js_scope,
      { "JavaScript scope", "mongo.element.value.js_scope",
      FT_NONE, BASE_NONE, NULL, 0x0,
      "Scope document for JavaScript evaluation", HFILL }
    },
    { &hf_mongo_database,
      { "database", "mongo.database",
      FT_STRING, BASE_NONE, NULL, 0x0,
      "the name of the database to run the command on", HFILL }
    },
    { &hf_mongo_commandname,
      { "commandName", "mongo.commandname",
      FT_STRING, BASE_NONE, NULL, 0x0,
      "the name of the command", HFILL }
    },
    { &hf_mongo_metadata,
      { "metadata", "mongo.metadata",
      FT_NONE, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_commandargs,
      { "CommandArgs", "mongo.commandargs",
      FT_NONE, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_commandreply,
      { "CommandReply", "mongo.commandreply",
      FT_NONE, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_outputdocs,
      { "OutputDocs", "mongo.outputdocs",
      FT_NONE, BASE_NONE, NULL, 0x0,
      NULL, HFILL }
    },
    { &hf_mongo_unknown,
      { "Unknown", "mongo.unknown",
      FT_BYTES, BASE_NONE, NULL, 0x0,
      "Unknown Data type", HFILL }
    },
  };

  static int *ett[] = {
    &ett_mongo,
    &ett_mongo_doc,
    &ett_mongo_elements,
    &ett_mongo_element,
    &ett_mongo_objectid,
    &ett_mongo_machine_id,
    &ett_mongo_code,
    &ett_mongo_fcn,
    &ett_mongo_flags,
    &ett_mongo_compression_info,
    &ett_mongo_sections,
    &ett_mongo_section,
    &ett_mongo_msg_flags,
    &ett_mongo_doc_sequence
  };

  static ei_register_info ei[] = {
     { &ei_mongo_document_recursion_exceeded, { "mongo.document.recursion_exceeded", PI_MALFORMED, PI_ERROR, "BSON document recursion exceeds", EXPFILL }},
     { &ei_mongo_document_length_bad, { "mongo.document.length.bad",  PI_MALFORMED, PI_ERROR, "BSON document length bad", EXPFILL }},
     { &ei_mongo_section_size_bad, { "mongo.msg.sections.section.size.bad",  PI_MALFORMED, PI_ERROR, "Bogus Mongo message section size", EXPFILL }},
     { &ei_mongo_unknown, { "mongo.unknown.expert", PI_UNDECODED, PI_WARN, "Unknown Data (not interpreted)", EXPFILL }},
     { &ei_mongo_unsupported_compression, { "mongo.unsupported_compression.expert", PI_UNDECODED, PI_WARN, "This packet was compressed with an unsupported compressor", EXPFILL }},
     { &ei_mongo_msg_checksum, { "mongo.bad_checksum.expert", PI_UNDECODED, PI_ERROR, "Bad checksum", EXPFILL }},
  };

  proto_mongo = proto_register_protocol("Mongo Wire Protocol", "MONGO", "mongo");

  /* Allow dissector to find be found by name. */
  mongo_handle = register_dissector_with_description("mongo", "Mongo Wire Protocol", dissect_mongo, proto_mongo);
  mongo_heur_handle = register_dissector_with_description("mongo_tcp", "Mongo Wire Protocol over TCP", dissect_mongo_tcp_heur, proto_mongo);

  proto_register_field_array(proto_mongo, hf, array_length(hf));
  proto_register_subtree_array(ett, array_length(ett));
  expert_mongo = expert_register_protocol(proto_mongo);
  expert_register_field_array(expert_mongo, ei, array_length(ei));
}


void
proto_reg_handoff_mongo(void)
{
  dissector_add_uint_with_preference("tcp.port", TCP_PORT_MONGO, mongo_heur_handle);
  /* ssl_dissector_add registers TLS as the dissector for TCP on the given
   * port, but Mongo uses the same port by default with or without TLS,
   * so we need to test for the non-TLS version as well.
   * If the TLS heuristic dissector detects TLS on this port, assume Mongo.
   */
  dissector_add_uint_with_preference("tls.port", TCP_PORT_MONGO, mongo_handle);
}
/*
 * Editor modelines
 *
 * Local Variables:
 * c-basic-offset: 2
 * tab-width: 8
 * indent-tabs-mode: nil
 * End:
 *
 * ex: set shiftwidth=2 tabstop=8 expandtab:
 * :indentSize=2:tabSize=8:noTabs=true:
 */
